A conventional cooking appliance of the hot air circulation type comprises a heating chamber for receiving a heating load, a heating device for heating said heating chamber, a compartment adjacent to said heating chamber, a fan housed in said compartment for circulating hot air through said heating chamber and said compartment, and a partition plate separating said compartment from said heating chamber and having blow-out ports and suction ports for circulating said hot air. A concrete example of such appliance is shown in FIGS. 1-3.
FIG. 1 is a side view, in section, of a conventional gas cooking appliance of the hot air circulation type. FIG. 2 is a front view, insection, of said appliance. FIG. 3 is a plan view, in section, of said appliance. A partition plate 2 at the back of a heating chamber 1 is provided with suction ports 3 disposed substantially in the middle and blow-out ports 4 disposed in the right and left peripheral regions. There is provided a compartment 8 having the partition plate 2, a combustion chamber 5, a circulation air heating chamber 6, and a circulation fan storing chamber 7. The combustion chamber 5 is positioned below the compartment 8 and is provided in the lower portion of its peripheral wall with an inlet port 9 for combustion air, is formed in its top wall with a combustion gas passage 10 opening to the circulation air heating chamber 6 and stores two main burners 11 and a pilot burner 12. The circulation air heating chamber 6 is formed so that its partition wall 8 surrounds the suction ports 3 of the partition plate 2, and it is bored with a suction part 14 opposed to the suction side of a circulation fan 13 installed in the circulation fan storing chamber 7. The right and left side walls of the circulation fan storing chamber 7 and the partition wall 8 extend to the partition plate 2, forming a blow-out line 15 for hot air communicating with the heating chamber 1.
In the arrangement described above, the hot air flowing out of the heating chamber 1 through the suction ports 3 formed substantially in the middle of the partition plate 2 and the combustion gas at high temperature from the burners 11 passing through the combustion gas passage 10 flow into the circulation air heating chamber 6 and are sucked by the circulation fan 13 through the suction port 14 to flow into the blow-out line 15. The two hot flows are sufficiently mixed by the combining and mixing action in this suction and blow-out process and by the stirring action of the circulation fan 13, thereby providing a hot air flow at high temperature and uniform in temperature throughout. The hot air flow at high temperature moves along the side wall of the circulation fan storing chamber 7 and is blown out into the heating chamber 1 through the blow-out ports 4, as shown in FIG. 3. Since the blow-out ports 4 are located adjacent the side walls of the heating chamber 1, the hot air flow blowing into the heating chamber 1 through the blow-out ports 4 moves along the side wall of the heating chamber 1, striking a door 16 and joining the other hot air flow, with the joint flow passing substantially through the middle of the heating chamber 1 and being sucked through the suction ports 3. Heating loads 18 placed on the peripheral regions of trays 17 are subjected directly to the hot air flow at high temperature passing out of the blow-out ports 4, so that they are liable to be overheated. Heating loads 18 placed on the middle regions of the trays 17 are heated by the hot air flow after heating the heating loads 18 placed on the peripheral regions of the trays 17. Since the hot air flows along the periphery of the heating chamber 1 before it reaches the middle region, it gradually loses some of its heat, producing a difference in the heating degree between the peripheral and middle regions. Further, if heating loads 18 of substantial height are placed around the periphery, they form an obstacle which makes it difficult for the hot air to flow to the middle region, so that the latter is less heated. Since the trays 17 are rotated, there is less difference in the degree of heating between the heating loads placed around the periphery.
It is seen from the above that with the conventional cooking appliance of the hot air circulation type, since the heating loads 18 placed on the peripheral regions of the trays are easily subjected to the hot air at high temperature blown out of the blow-out ports 4, they are overheated and dried causing them to lose the moisture in their surfaces, become hard, while the heating loads 18 placed on the middle regions are subjected to hot air at lower temperature, resulting in insufficient heating which makes them washy and tasteless. Thus, there has been a large difference in the degree of heating between the middle and peripheral regions.